Polychlorinated biphenyls, or "PCB's" were long used as dielectric fluids in electrical equipment because these materials have excellent heat stability, are non-flammable in nature, have low volatility and a good viscosity characteristic at operation temperatures. Because of their environmental persistence, however, continued manufacture, import or use in the United States was banned under the Toxic Substances Control Act of 1976, and the U.S. Environmental Protection Agency was directed to promulgate rules and regulations for their removal from the economy.
As of July 1, 1979, EPA regulations defined as "PCB-contaminated" any material containing more than 50 ppm of a mono-, di-, or polychlorinated biphenyl. The regulations permitted the disposal of PCB-contaminated materials by either incineration in an approved manner or in an approved landfill, but such procedures have rarely proven acceptable to community neighbors.
Since considerable fractions of the transformer oils, e.g., refined asphaltic-base mineral oil, or heat exchange oils, e.g., hydrogenated terphenyls, now in service are PCB-contaminated, the problem of disposing of PCB-contaminated hydrocarbon oils in an effective manner presents a serious challenge.
Various techniques for degrading the polyhalogenated hydrocarbons in such oils have been proposed. Most techniques are too lengthy and/or complex to provide a practical solution to the problem of PCB-contaminated oil. However, processes disclosed by Brunelle in U.S. Pat. Nos. 4,353,793, 4,351,718 and 4,410,422 provide rapid and effective degradation of PCB's in such oils. These processes utilize alkali metal hydroxides in combination with polyalkyleneglycols and/or monoalkyl ethers of polyethylene glycols. The above patents are assigned to the same assignee as the present invention and are incorporated herein by reference.
These reagents are insoluble in the contaminated transformer oil and are difficult to handle in conventional equipment. For example, the alkali metal hydroxide/glycol reagents and reaction products form a sticky viscous mass within the process equipment. This sticky viscous mass adheres to the surfaces of the process equipment such as the reactor chamber walls, filters, heat exchangers, conduits and valves. When neglected, this sticky mass will accumulate and can foul downstream equipment, such as filters, heat exchangers, etc. In addition, accumulation in the reactor reduces the heat transfer through the reactor walls. Such accumulation may require the process to be interrupted and the equipment cleansed by manually scraping and washing the same.
The present invention provides a method for removing polyhalogenated hydrocarbons from transformer oil without accumulation of the sticky viscous mass within the equipment utilized. The present invention is based on the discovery that the addition of small quantities of water upon completion of the reaction liberates the sticky viscous mass that adheres to the equipment surfaces.